Leave Mod-a and Mod-z to a host element focused beside the editor

[janglad]

Summary

The document key handler claimed Mod-a, Mod-z and Mod-Shift-z for any mounted editor that still had a caret, even while a host element held focus. A host's own undo or select-all never saw the key: the editor undid its last edit and stopped propagation in capture.

HOST9 already says focus on a host element is the host's. Keys now follow the same ownership.

 shouldHandleEditorKeyboardEvent
   …
+  if document shortcut (Mod-a, Mod-z, Mod-Shift-z)
+     and activeElement is neither inside root nor a wrapper of root
+    return false
   if hasMappedDomSelection → true
   if document shortcut → isDocumentSelection(selection, true)

Unchanged: focus on the body, or on a focusable wrapper around the root, still routes these keys to the editor.

Spec: HOST9 in spec/rules/host.md and the gate note in spec/packages/rendering/dom.md are amended in this PR.

Evidence

• Before: textEntryTarget.host9.test.ts, a focused host <button> beside the root with Mod-z or Mod-a: shouldHandleEditorKeyboardEvent returned true.
  After: returns false for Mod-a, Mod-z and Mod-Shift-z. Body focus and a focused wrapper still return true.
• pen-dom typecheck and the src/utils tests pass. The full pen-dom, pen-react and pen-vue suites passed on the previous revision, which differed only by also covering Mod-y.

Merge Danger

Door: two-way

Patch changeset for @input/pen-dom, Breaking: no.

Blast Radius: keyboard-routing

• A host that relied on Mod-z or Mod-a reaching the editor while one of its own elements held focus (a toolbar button mounted outside the root that keeps focus after a click) now receives the key itself.
• A leftover range or block selection in an unfocused editor can still claim other keys (Backspace, Delete, arrows) under host focus. Unchanged here.
• An editor inside a shadow root is not recognised as containing or contained, since contains does not cross the boundary.

---

Note

Medium Risk
Changes capture-phase routing for Mod-a/Mod-z/Mod-Shift-z; hosts that depended on editor undo/select-all while their own focused chrome sat outside the root will now receive those keys instead.

Overview
Fixes HOST9 keyboard ownership so Mod-a, Mod-z, and Mod-Shift-z are not stolen by the editor’s capture-phase document handler when focus sits on a host element beside the editor root (not inside the root and not on a wrapper that contains the root). Previously, any mounted editor with a leftover caret still routed those shortcuts to undo/select-all even while a host button or control held focus.

shouldHandleEditorKeyboardEvent in textEntryTarget.ts now returns false for document shortcuts in that focus case, before mapped-DOM-selection and selection-based routing. Unchanged: focus on document.body or on a focusable wrapper around the root still routes Mod-a/Mod-z to the editor.

Adds textEntryTarget.host9.test.ts, a patch changeset for @input/pen-dom, and spec updates in spec/rules/host.md and spec/packages/rendering/dom.md.

^{Reviewed by Cursor Bugbot for commit 56effc9. Bugbot is set up for automated code reviews on this repo. Configure here.}

[janglad]

bugbot run

[cursor]

✅ Bugbot reviewed your changes and found no new issues!

Comment @cursor review or bugbot run to trigger another review on this PR

^{Reviewed by Cursor Bugbot for commit 56effc9. Configure here.}